Preforming the reinforcement allows the strength of the reinforcement to be designed in accordance with the ultimate loading to be experienced by the finished component. That is, the position and direction of the reinforcing fibers can be aligned and Positioned as desired to achieve the desired structural strength of the finished component. The reinforcement can be made from a wide variety of different reinforcing materials, but typically glass fibers and carbon fibers are used.
In the molding of such a component, it is essential that the plastics resin which is introduced to the mold should thoroughly wet the reinforcement. The resin is conventionally introduced through a gate and flows through the preform to an edge of the mold. Air is displaced through the edges of the mold by the advancing resin front.
Various processes are known for molding reinforced plastics components in this way. The majority of such components fall under the category referred to as resin transfer molding (RTM) where a polymerized resin is introduced into the mold.
Such known molding methods however have a number of disadvantages. In order to ensure thorough wetting of the preform, particularly around the edges of the mold, many known processes require a slow cure time so that the resin remains liquid and can flow over a long period. Long cycle times however are disadvantageous for volume production.
Other methods use an excess volume of resin so that resin bleeds out of the mold around the edges, thus ensuring that the reinforcement at the edges of the mold is fully wetted, but requiring subsequent trimming of considerable flash and resultant wastage.